Steam generator protector

ABSTRACT

In a liquid metal steam generator having a plurality of parallel metal tubes welded between at least a pair of tube sheets for the passage of fluid therethrough, said tubes being housed in a container. The invention comprises a protective metal cylinder fabricated of a material that resists the corrosive-erosive effects of sodium-water reaction products which surrounds a weld of each of said tubes and a shield between all of the tubes and the container to prevent catastrophic damage to the adjacent tubes and the container in the event of leak in one of the tubes.

STEAM GENERATOR PROTECTOR Edward B. Ash, Canoga Park, Calif.

North American Rockwell Corporaltion, Pittsburgh, Pa.

Filed: Oct. 13, 1969 Appl. No.: 865,839

Inventor:

Assignee:

US. Cl. ..165/134, 122/32, 165/158,

176/65 Int. Cl. ..F28f 19/00 Field of Search 165/134, 158;

References Cited UNITED STATES PATENTS 5/1964 Esleeck ..165/134 [111 3,726,339 1 Apr. 10, 1973 FOREIGN PATENTS OR APPLICATIONS 1,205,121 11/1965 Germany ..l65/158 Primary Examiner-Albert W. Davis, Jr.

Attorney-L. Lee l-lumphries, Thomas S. MacDonald and Henry Kolin ABSTRACT In a liquid metal steam generator having a plurality of parallel metal tubes welded between at least a pair of tube sheets for the passage of fluid therethrough, said tubes being housed in a container. The invention comprises a protective metal cylinder fabricated of a material that resists the corrosive-erosive effects of sodium-water reaction products which surrounds a weld of each of said tubes anda shield between all of the tubes and the container to prevent catastrophic damage to the adjacent tubes and the container in the event of leak in one of the tubes.

4 Claims, 2 Drawing Figures PATENTED 3.726.339

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ATTORNEY STEAM GENERATOR PROTECTOR BACKGROUND OF THE INVENTION The use of walls or partitions to separate different fluids is well known; for example, a tube wall or a tube sheet separates the fluids passing through a heat' exchanger. In a shell and tube heat exchanger a primary fluid such as a liquid metal flows through a chamber defined by separate tube sheets that are spaced apart by a suitable shell member. US. Pat. No. 3,176,761, issued Apr. 6, 1965, shows one form of shell and tube heat exchanger. The tube sheets may have individual integral or welded tubular extensions or projections that are then metallurgically joined, such as by welding, to opposite ends of tubes forming a tube bundle through which a secondary fluid such as water or steam flows. The tube walls and tube sheets therefore separate the primary and secondary fluids in a heat exchanger.

The tube sheets and tubes are constructed of a metal that can withstand the high operating temperature and pressure. However, if there should be a localized leak that allows the water to mix with the molten metal, for example, sodium, chemical reactions and high velocities and temperatures are generated which can damage adjacent tubes and/or the container, leading to a propagating type damage of the entire assembly. The entire assembly could be manufactured from a material such as Incoloy which is relatively resistant to a reaction and to erosive damage such as would occur when sodium and water (or steam) are mixed; however, the

metal is more costly and has other materials problems.

dividually located shields that surround each welded tube to the tube sheet, there is an annular casing that surrounds all of the tubes and is spaced from the interior walls of the steam generator housing so that any leak that might occur cannot quickly propagate through the walls of the casing, possibly destroying the entire heat exchanger as well as the surrounding components. The shields can be used over the entire tube length or just locally around the weld, which is judged to be the high risk area.

An advantage over the prior art is the ability to confine a leak path of fluid into the surrounding molten metal so that the entire heat exchanger is not destroyed. If a leak path should occur, instrumentation can be provided for its detection before secondary failures occur and the heat exchanger can be shut down and removed and subsequently repaired or replaced with a substitute heat exchanger.

Another advantage over the prior art is the capability to construct a liquid metal steam generator from a relatively inexpensive and more reliable material when a means to protect the weak points, i.e., the, welded State-of-the-art heat exchangers are disadvantaged by the possible propagation of damage from tube to tube or to the container when a leak occurs between the molten metal and water (or steam).

Therefore, it is an object of this invention to provide a protective means to'inhibit this failure propagation mode in case of a leak between the water and molten metal.

More specifically, it is an object of this invention to provide a tubular shield that surrounds the weld between a tube and tube sheet to inhibit direct impingement of leaking fluid upon the adjacent tube and the inevitable reaction between the water and the molten metal so that the reaction is contained within the area that the particular tube is located, thus either eliminating or slowing down secondary tube or container failures.

SUMMARY OF THE INVENTION Briefly, in accordance with one form of the invention, an improved liquid metal steam generator is proposed wherein the individual weld joints within the heat exchanger are protected by an annular spaced shield that surrounds the individual weld joints yet does not contact the joint so that if a leak path should occur between the water or steam and the primary fluid, i.e., liquid molten metal, the reaction products do not directly impinge on adjacent tubes or housing. The shield is constructed of a material that is relatively resistive to a reaction resultant from high velocity water or steam into the molten metal so that the leak path cannot quickly propagate to the adjacent tubes or through the outer wall of the housing. A further safeguard is provided in that, in addition to the injoints, includes an annular shroud which encompasses but does not contact the welded joint. The protective shroud can be fabricated of a relatively expensive material since little of the material is needed to fabricate the protective device.

DESCRIPTION OF THE DRAWINGS bodiment of the invention illustrating the individual tube protectors as well as the annular shroud between the tube stack and the tube housing,

FIG. 2 is a view taken along lines 2-2 of FIG. 1 particularlypointing out the spatial relationship of the tube protector shroud and tube as well as the shroud surrounding the tube bundle between the bundle and the outer casing.

Referring now to FIG. 1, the basic steam generator 10 consists of a housing 12, a tube sheet 14, a primary fluid inlet 16, and outlet 18 and a plurality of tubes 20. Each of the tubes 20 are metallurgically joined (welded) to tube sheet 14 at juncture 22, adjacent tube sheet stubs 24.

A primary fluid 26, for example, liquid molten sodium, enters inlet 16 and fllls chamber 28, thereby providing a heat source for the plurality of tubes 20. The liquid sodium exits outlet 18. A secondary fluid, for example, water or steam, enters cavity 30 which is in communication with each of the tubes 20 at entrance In operation, liquid sodium enters inlet 16, surrounding each of the tubes 20 while the secondary fluid (water) enters ports 32 communicating with each of the tubes 20. The liquid sodium vaporizes the water turning it to steam under extremely high pressure and the liquid sodium, in turn, leaves exit port 18 considerably cooler than the temperature at which it enters. If a crack or leak should occur in the weld 22, 1

steam under extremely high pressures would escape through the crack into the sodium resulting in high velocities, high temperatures, and chemical reaction products which are capable of causing further damage to adjacent tubes or housing 12.

To guard against a catastrophic destruction an annular sleeve 34 is joined to the tube sheet 14 at juncture 36. The sleeve 34 is concentric with and annularly spaced from the tubes 20 and the rim of the sleeve 35 extends a set distance above the welded tube joint 22. An annular gap 38 is formed between the outside of the tube 20 and the interior wall of the sleeve 34. The sleeve 34 is fabricated from a material that is relatively resistant to the reaction products of water (steam) and sodium resultant from a leak through the weld joint 22. The material of the tube 34 can be, for example, Incoloy, which has shown a resistance to the foregoing reaction. The purpose of the sleeve 34 is to inhibit a sodium water reaction resultant from a leak through the wall 22 so that the reaction does not propagate to the adjacent tubes, therefore destroying, in turn, those adjacent tubes. Suitable detectors within the steam generator can be installed (not shown) within the chamber 28 or on the outlet line 18 to detect any such reaction due to a leak which could immediately then shut down the heat exchanger.

Surrounding the entire tube bundle and spaced from the interior walls of generator 12 and within chamber 28 is an annular shield 40 which is metallurgically bonded to tube sheet 14 at its base in a manner similar to the weld protectors 34. Shield 40 prevents the propagation of a catastrophic failure from penetrating housing 12. Thus it can be seen that any failure in the steam generator will not damage surrounding components within.

The partial section shown in FIG. 2 clearly shows the spatial relationship between the shield 34 and the tubes 20. If the tube shield 34 were adjacent the tube sheet stub 24 and the tube 20, any expansion or contraction between the tube 20 and the tube sheet 14 would be transmitted to the sleeve 34, possibly causing it to fail, along with the weld 22. Thus the reason for the annular space between shield 34 and tube 20. The annular space also allows the reaction products to reach an external detector. Any contraction or expansion is independent of the shield 34 since it is a unit in itself. The annular space 38 allows the damaging local reactions to be confined within this space in the event of a leak. Shield 40 is spaced (42) from the housing 12 for the same reason, any contortions that housing 12 might sustain would not be transmitted to the shield, therefore, providing a maximum protection of the housing and the surrounding components.

For example, in a typical heat exchanger where the tubes 20 are 0.625 of an inch in diameter the shield 40 extends a distance of approximately 7 inches above the tube weld joints and has a wall thickness of 0.125 of an inch with an annular spacing (42) of about 0.125 of an inch.

It should be noted here that there are other types of primary fluids than sodium that can be used and there are other types of secondary heat exchange fluids passing'through the tubes that can be used for the heat exchange function.

Iclaim:

1. In a heat exchanger apparatus, the apparatus including a plurality of spaced tubes having first and second ends for passing fluid therethrough suspended between at least a pair of tube sheets, said tube sheets having a plurality of inwardly facing tube sheet stubs extending from said tube sheets, said first and second ends of said tubes being welded to said tube sheet stubs, the apparatus being contained in a housing, the apparatus further comprising protection means at the ends of each of said tubes for individually guarding the welded joint between said tube sheet stubs and each of said tubes, said protection means comprising an annular ring means welded to an adjacent tube sheet and extending beyond the weld joint a set distance toward the other tube sheet and spaced from said tubes at the weld joint forming a discrete chamber between the tubes and the ring means to protect the adjacent tubes in the event of a catastrophic reaction resultant from a leak from said weld joint, said protection means serving to inhibit said catastrophic reaction from an invasion of a first fluid from the interior of said tubes into a second fluid contained in said housing and surrounding said tubes.

2. The invention as set forth in claim 1 further including a second protection means comprising a shield generally contiguous to said housing substantially impervious to a reaction from an invasion of a first fluid into said liquid metal, said shield being spaced from said tubes welded to the tube sheet and said housing to contain and inhibit a catastrophic reaction within said housing.

3. In a heat exchanger apparatus using liquid metal as a heat transfer medium, the apparatus including a plurality of spaced tubes having first and second ends for passing fluid therethrough suspended between at least a pair of tube sheets, said tube sheets having a plurality of inwardly facing tube sheet stubs extending from said tube sheets, said first and second ends of said tubes being welded to said tube sheet stubs, the apparatus being contained in a housing, the apparatus further comprising:

a first protection means surrounding the ends of said tubes, said protection means comprising an annular ring having a base portion and a rim portion, said ring being concentric with each tube, the ring being welded to an adjacent tube sheet and extending beyond the weld joint of the tube and tube sheet stub a set distance toward the other tube sheet and spaced from said tubes at said tube sheet stub weld joint forming a discrete chamber between the tubes and the ring,

second protection means comprising a shield generally contiguous to said housing,

said shield being spaced from the tubes and said housing, wherein said first and second protection means protects said heat exchanger in the event of a catastrophic reaction resultant from a leak through a tube sheet stub weld joint.

4. In a heat exchanger apparatus using liquid metal as a heat transfer medium, the apparatus including a plurality of spaced tubes having first and second ends for passing a water-containing fluid therethrough, said tubes being suspended between and welded to at least a pair of tube sheets forming a plurality of weld joints exposed to said liquid metal, the apparatus being contained in a housing, the apparatus further including protection means comprising a shield generally contiguous to said housing bonded to a tube sheet said shield being radially outward from said tube weld joints and extending to a point above each of the tube joints and being exposed to liquid metal on each side thereof,

being spaced from said tubes and said housing to contain and inhibit a catastrophic reaction within said housing from any leak in said weld joints and including means forming apertures in said shield to allow flow of said shield being made of a material substantially im- 5 liquid metal therethmugh- 

2. The invention as set forth in claim 1 further including a second protection means comprising a shield generally contiguous to said housing substantially impeRvious to a reaction from an invasion of a first fluid into said liquid metal, said shield being spaced from said tubes welded to the tube sheet and said housing to contain and inhibit a catastrophic reaction within said housing.
 3. In a heat exchanger apparatus using liquid metal as a heat transfer medium, the apparatus including a plurality of spaced tubes having first and second ends for passing fluid therethrough suspended between at least a pair of tube sheets, said tube sheets having a plurality of inwardly facing tube sheet stubs extending from said tube sheets, said first and second ends of said tubes being welded to said tube sheet stubs, the apparatus being contained in a housing, the apparatus further comprising: a first protection means surrounding the ends of said tubes, said protection means comprising an annular ring having a base portion and a rim portion, said ring being concentric with each tube, the ring being welded to an adjacent tube sheet and extending beyond the weld joint of the tube and tube sheet stub a set distance toward the other tube sheet and spaced from said tubes at said tube sheet stub weld joint forming a discrete chamber between the tubes and the ring, a second protection means comprising a shield generally contiguous to said housing, said shield being spaced from the tubes and said housing, wherein said first and second protection means protects said heat exchanger in the event of a catastrophic reaction resultant from a leak through a tube sheet stub weld joint.
 4. In a heat exchanger apparatus using liquid metal as a heat transfer medium, the apparatus including a plurality of spaced tubes having first and second ends for passing a water-containing fluid therethrough, said tubes being suspended between and welded to at least a pair of tube sheets forming a plurality of weld joints exposed to said liquid metal, the apparatus being contained in a housing, the apparatus further including protection means comprising a shield generally contiguous to said housing bonded to a tube sheet said shield being radially outward from said tube weld joints and extending to a point above each of the tube joints and being exposed to liquid metal on each side thereof, said shield being made of a material substantially impervious to water-liquid metal reaction products and being spaced from said tubes and said housing to contain and inhibit a catastrophic reaction within said housing from any leak in said weld joints and including means forming apertures in said shield to allow flow of liquid metal therethrough. 